Method for forming adhesive layer

ABSTRACT

In a method for forming an adhesive layer on the surface of a workpiece before the formation of a coating film containing a powder on the workpiece, the present invention provides a method for forming the adhesive layer having a desired thickness. This object is achieved by the following method: An adhesive layer formation medium m 1  coated with an adhesive material is made to collide with a workpiece W so that the adhesive material is transferred from the adhesive layer formation medium m 1  to the workpiece W and forms an adhesive layer on the workpiece. An adhesive layer having a desired thickness can be formed on the workpiece by regulating the thickness of the adhesive material applied to the surface of the adhesive layer formation medium (i.e. the amount of the adhesive material held by a single adhesive layer formation medium). This enables the thickness of the powder coating as the final product to be controlled as desired.

TECHNICAL FIELD

As disclosed in the Japanese Unexamined Patent Publication Nos.H05-302176, H07-112160, H07-136577 and other patent applications, theapplicant of the present invention has proposed a powder-coating methodin which a workpiece (i.e. an object or a part to be coated with powder)having an adhesive layer formed on its surface, fine particles ofpowder, a powder-coating medium and so on are vibrated with a vibratorso as to apply the powder to the surface of the workpiece via thepowder-coating medium. This method can be used to paint the body orother elements of electronic devices, such as cellular phones ornotebook computers. The present invention relates to a method forforming an adhesive layer on the surface of a workpiece, which isperformed as a step of the above-described powder-coating method.

BACKGROUND ART

Currently, various kinds of liquid thermosetting resins are used as anadhesive material for forming an adhesive layer. Forming a uniformadhesive layer on the surface of a workpiece requires a resin having ahigh degree of fluidity. Therefore, the resin used for this purpose isusually dissolved into, diluted with or dispersed in an organic solvent,water or other solvent. Using the liquid resin prepared by diluting aresin with an organic solvent or a similar solvent as described above,an adhesive layer is formed on the surface of the workpiece by dippingthe workpiece in a reservoir containing the resin, or by spraying theresin onto the workpiece. An example of the liquid resins currently usedis a thermosetting epoxy resin, containing 97% resin and 3% curingagent, diluted with methyl ketone.

DISCLOSURE OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

In the above-described powder-coating method, the powder is directly, orvia the powder-coating medium, applied to the workpiece having theadhesive layer formed on its surface, and then the powder is pressedonto or into the adhesive layer by the beating action of thepowder-coating medium. Along with this process, the adhesive materialconstituting the adhesive layer, which is now covered with the powder,is extruded up to the surface of the powder by the beating action of thepowder-coating medium. The adhesive material thus extruded also receivesthe collision of the powder-coating medium, whereby the powder held onthe powder-coating medium is transferred to the workpiece. Thus, thepowder is continuously applied to the workpiece. Such a powder applyingprocess, or a powder coating process, is finished when the adhesivematerial constituting the adhesive layer can no longer be extruded up tothe surface of the powder by the beating action of the powder-coatingmedium onto the workpiece. Therefore, the thickness of the adhesivelayer applied to the workpiece decisively influences the thickness ofthe powder coating formed on the workpiece.

As explained previously, the adhesive layer on the surface of theworkpiece is formed by dipping the workpiece in a reservoir containing aliquid resin diluted with a solvent, or by spraying a liquid resindiluted with a solvent onto the surface of the workpiece. Use of such adipping or spraying means, however, makes it difficult to regulate thethickness of the liquid resin applied to the workpiece, which means thatit is difficult to form a powder coating having a desired thickness onthe workpiece. Another problem that further increases the difficulty inthe regulation of the thickness of the adhesive layer formed on theworkpiece exists in that the solvent should be removed from the liquidresin applied to the workpiece. Moreover, if the liquid resin is appliedusing a dipping or spraying means, the liquid resin applied to thesurface of the workpiece is locally collected and forms one or morepools on the surface of the workpiece, which causes the adhesive layerformed on the surface of the workpiece to be uneven in thickness.

After the liquid resin is applied to the surface of the workpiece, it isnecessary to remove the solvent and other components. Therefore,conventionally, a heat treatment is performed on the workpiece coatedwith the liquid resin to evaporate the solvent and other components.This method takes a long time for the formation of the adhesive layerand is problematic with respect to the conservation of energy.

Furthermore, if the thermosetting resin has a low curing temperature, itis impossible to perform the heat treatment to evaporate the solvent andother components, and the resin needs to be left at room temperature.This requires a longer time for the adhesive layer to be formed.

Thus, an object of the present invention is to solve the above-describedproblems relating to the conventional method for forming an adhesivelayer.

MEANS FOR SOLVING THE PROBLEMS

To solve the above-described problems, a method for forming an adhesivelayer according to the present invention is characterized in that theadhesive layer is formed on a workpiece by making an adhesive layerformation medium coated with an adhesive material collide with theworkpiece so that the adhesive material applied to the adhesive layerformation medium is transferred to the workpiece.

Another method for forming an adhesive layer according to the presentinvention is characterized in that the adhesive layer formation mediumcoated with an adhesive material and a workpiece are put into acontainer, and an adhesive layer is formed on the workpiece by vibratingthe adhesive layer formation medium or the workpiece, or by stirring theadhesive layer formation medium and the workpiece.

In the above-described methods for forming an adhesive layer, it ispreferable to form the adhesive layer on the surface of the workpiecehaving little or no adhesive material applied to it.

In the above-described methods for forming an adhesive layer, it ispreferable to maintain the thickness of the adhesive layer formed on theadhesive layer formation medium within a specific range so that theadhesive layer to be formed on the workpiece has a uniform thickness.

The adhesive material may desirably contain a liquid material. Apreferable example of the liquid material is a liquid resin, which maypreferably contain a curing agent. The adhesive material may alsocontain spacer particles. Finally, the adhesive material desirablyconsists of a substantially non-volatile material.

A powder-coating method according to the present invention ischaracterized in that a powder coating is formed on the surface of aworkpiece by applying fine particles of powder to an adhesive layerformed on the surface of the workpiece by one of the above-describedmethods for forming an adhesive layer. The adhesive material maypreferably contain spacer particles, where the spacer particlespreferably consist of particles of the powder.

EFFECT OF THE INVENTION

With the above-described constructions, the present invention yields thefollowing effects.

According to the present invention, an adhesive layer is formed on theworkpiece by making an adhesive layer formation medium coated with anadhesive material having a thickness within a specific range collidewith the workpiece so that the adhesive material applied to the adhesivelayer formation medium is transferred to the workpiece. This methodenables an adhesive layer having a desired thickness to be formed on theworkpiece by regulating the thickness of the adhesive layer applied tothe surface of the adhesive layer formation medium, or by regulating theamount of the adhesive material held by a single adhesive layerformation medium. Therefore, in the subsequent powder coating process, apowder coating having a desired thickness can be formed on the surfaceof the workpiece.

Also, according to the present invention, an adhesive layer is formed ona workpiece by making an adhesive layer formation medium coated with anadhesive material collide with the workpiece so that the adhesivematerial is transferred to the workpiece. This method prevents theformation of a pool that is observed if the workpiece is dipped in areservoir containing a liquid resin used as the adhesive material or theliquid resin is sprayed onto the workpiece as in the conventionalmethods for forming an adhesive layer. Thus, an adhesive layer having auniform thickness on the workpiece is obtained.

The presence of the spacer particles on the surface of the adhesivelayer formation medium prevents the medium from being trapped onto theworkpiece. It also improves the smoothness of the surface of theadhesive layer to be formed on the workpiece.

Since there is no need to use any solvent or similar component to beremoved after the application of the adhesive material, the presentinvention not only simplifies the process of forming an adhesive layerbut also realizes the conservation of energy and the prevention ofpollution. Furthermore, the elimination of the heat treatment forremoving the solvent and other components increases the degree offreedom of the curing agent and the base resin available.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view including a partial section of a vibrator with acontainer attached to it as an example of the means for applying anadhesive material to an adhesive layer formation medium.

FIG. 2 is a schematic perspective view of an adhesive layer formationmedium having an adhesive layer formation medium applied and spacerparticles attached to it.

FIG. 3 is a front view including a partial section of an adhesive layerformation device for forming an adhesive layer on a workpiece.

FIG. 4 is a front view including a partial section of another embodimentof an adhesive layer formation device for forming an adhesive layer on aworkpiece.

EXPLANATION OF NUMERALS

C—container

V—vibrator

W—workpiece

m1—adhesive layer formation medium

m2—adhesive material

m3—spacer particle

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the method for forming an adhesive layer according to thepresent invention are described. It should be noted that embodiments arenot restricted to the following ones described and may take any form aslong as it is within the scope of the present invention.

In the present invention, a layer of adhesive material is created on thesurface of the adhesive layer formation medium by applying an adhesivematerial or an adhesive material containing a liquid material to themedium. This layer, called the adhesive layer hereinafter, consists of amaterial that hardly or never evaporates during the process of formingan adhesive layer on the workpiece.

Various kinds of liquid materials, including liquid resins, areavailable as the adhesive material constituting the adhesive layer. Inaddition to liquid resins, examples of the liquid materials includewater glass, gelatin, glue and lacquer. For the liquid resin, there arevarious kinds of resins available, including epoxy resin, polyesterresin, acrylic resin, polyurethane resin, fluororesin and melamineresin. For a liquid material having a high viscosity, it is allowable toadd a compound of a certain kind of resin as a viscosity reducer.

A curing agent may be added to the liquid resin used as the adhesivematerial. It is also possible to add spacer particles to the liquidmaterial used as the adhesive material constituting the adhesive layer.

Examples of the curing agent include dicyandiamide, imidazole,isocyanate, acids and their anhydride.

The spacer particle is a fine particle made of silica, alumina,zirconia, aluminum hydroxide, various kinds of metal and resins, and soon. The size and load of the particles should be appropriatelydetermined according to the form and size of the adhesive layerformation medium. In a preferable case, the diameter is about 1 to 20 μmand the volume percentage in the adhesive material is about 5 to 30%.For the spacer particles, it is desirable to use fine particles ofpowder that will constitute the powder coating to be obtained as thefinal product.

Examples of the material for the adhesive layer formation medium includeiron, carbon steel, other alloy steels, copper and its alloy, aluminumand its alloy, and other kinds of metal and alloy, Al₂O₃, SiO₂, TiO₂,ZrO₂, SiC and other kinds of ceramic, glass, hard glass and so on. Thesize, material and other properties of the adhesive layer formationmedium can be appropriately determined according to the shape and sizeof the workpiece, the material and other properties of the powderconstituting the film to be formed on the workpiece, and other factors.Plural types of adhesive layer formation media differing in size andmaterial may be mixed together. It is possible to perform a surfacetreatment or surface coating on the adhesive layer formation medium. Theadhesive layer formation medium can take various shapes: sphere,ellipse, cube, triangle pole, cylinder, circular cone, triangularpyramid, rectangular pyramid, rhombohedron and other indefinable shapes.Each of the adhesive layer formation media having the above-listedshapes may be used independently, or two or more types may be mixedtogether. As for the size of the adhesive layer formation medium, apreferable range is 0.3 to a few millimeters in diameter if the mediumis spherical.

An example of the device available for applying a mixture for forming anadhesive layer to the adhesive layer formation medium is shown in FIG.1, in which a container C is attached to a vibrator V. In FIG. 1, thevibrator V has a base v1 supporting a vibrating plate v3 via coilsprings v2, and the container C is mounted on the vibrating plate v3. Amotor v4 is located under the vibrating plate v3, and a weight v6 iseccentrically connected to the output shaft v5 of the motor v4. In thisconstruction, when the motor v4 is energized, the weight v6 rotates inan eccentric manner, thereby vibrating the container C mounted on thevibrating plate v3.

A mixture of the adhesive layer formation medium and the liquid materialused as the adhesive material, a mixture of the adhesive layer formationmedium and the liquid resin used as the adhesive material with a curingagent added to it, or a mixture of the adhesive layer formation mediumand the liquid material as the adhesive material with spacer particlesadded to it, is put into the contained C attached to the vibrator V, asshown in FIG. 1, and mixed together. As a result, the surface of theadhesive layer formation medium is evenly covered with the liquidmaterial, the liquid resin with the curing agent added to it, or theliquid material with the spacer particles added to it. Thus, an adhesivelayer formation medium having an adhesive layer on its surface isobtained. Instead of using a vibrator V having a container C as shown inFIG. 1, it is possible to put the mixture into a normal container andstir it with a stirrer to form an adhesive layer on the surface of theadhesive layer formation medium.

FIG. 2 schematically shows an adhesive layer formation medium having anadhesive layer formed by one of the above-described processes in which amixture of the adhesive layer formation medium, the spacer particles andthe adhesive material is put into the container C attached to thevibrator V. The adhesive layer formation medium m1 thus produced iscoated with the adhesive material m2, and a predetermined amount of thespacer particles m3 coated with the adhesive material are adhered to themedium.

The thickness of the adhesive layer formed on the surface of theadhesive layer formation medium can be arbitrarily determined byappropriately regulating the amount of the liquid material put into thecontainer C as the adhesive material with respect to the total surfacearea of the adhesive layer formation medium loaded into the container C.

As shown in FIG. 3, the adhesive layer formation medium having theadhesive layer formed as described above is put in the container Cattached to the vibrator V shown in FIG. 1, and workpieces W havinglittle or no adhesive material applied to it is thrown into it. Then,the vibrator V is energized to vibrate the container C holding theadhesive layer formation medium m1 coated with the adhesive layer andthe workpieces W having little or no adhesive material applied to it.This operation makes the adhesive layer formation medium m1 coated withthe adhesive layer collide with or come into friction with theworkpieces W. In some cases, the term “friction” might be more suitableto describe the action of the adhesive layer formation medium againstthe workpieces W. However, in the present description, the term“collision” is also used to refer to an action that should be usuallyregarded as “friction.” As a result of the collision, the adhesive layerformed on the adhesive layer formation medium m1 is transferred to theworkpieces W. In other words, the workpieces W scrape the adhesive layerfrom the adhesive layer formation medium m1, and the adhesive layer thusscraped forms an adhesive layer on the surface of the workpieces W.Thus, an adhesive layer having a predetermined thickness is formed onthe workpieces W by repetitive processes of transferring the adhesivelayer from the adhesive layer formation medium m1 to the workpieces Wand then separating the adhesive layer formation medium m1 from theworkpieces W.

The same adhesive layer can be also formed on the surface of theworkpieces W by stirring the adhesive layer formation medium m1 coatedwith the adhesive layer and the workpieces W, using a stirrer.

In each of the processes described above, it is possible to control thethickness of the adhesive layer formed on the workpiece by regulatingthe thickness of the adhesive material applied to the surface of theadhesive layer formation medium, or the amount of the adhesive materialheld by each particle of the adhesive layer formation medium, and alsoregulating the viscosity of the adhesive material forming the adhesivelayer and the amount of the spacer particles.

The amount of the adhesive layer formation medium needs to besufficiently large, irrespective of the thickness or size of theadhesive layer to be obtained. To uniformly apply the adhesive materialto the entire surface of the workpiece on which the adhesive layershould be formed, it is necessary to allow the adhesive layer formationmedium coated with the adhesive material to evenly beat or rub thesurface of the workpiece a large number of times.

Thus, the present invention enables an adhesive layer having a desiredthickness to be formed on the workpiece. Therefore, it is possible toregulate the thickness of the powder coating formed on the surface ofthe workpiece, using a powder-coating device to be described later.

The adhesive material constituting the adhesive layer formed on theadhesive layer formation medium does not contain any substance to beremoved by an evaporation process. Accordingly, the adhesive layerformed on the workpiece does not contain such a material, either.Therefore, there is no need to heat the workpiece to evaporate anysolvent or other component. As a result, the total time required for theformation of the adhesive layer becomes shorter than that required inthe case of forming an adhesive layer on the workpiece by a conventionalmethod. It also contributes the conservation of energy and theprevention of pollution. There is no possibility that the thickness ofthe adhesive layer formed on the workpiece will change due toevaporation. Therefore, the thickness of the adhesive layer can beeasily controlled.

As opposed to the conventional method for forming an adhesive layer on aworkpiece, there is no need to perform a heat treatment. Thisfacilitates the use of a thermosetting resin having a low curingtemperature as the adhesive material.

As shown in FIG. 2, it is preferable to use an adhesive layer formationmedium m1 coated with an adhesive material m2 and having spacerparticles m3 coated with the adhesive material. In the followingdescription, the adhesive layer formation medium m1, the adhesivematerial m2 and the spacer particles m3 are integrally referred to asthe “adhesive/spacer medium m0.” Similar to the case described earlier,the adhesive/spacer medium m0 is put in the container C attached to thevibrator V shown in FIG. 3, and workpieces W having little or noadhesive material applied to it is thrown into it. The container Cholding the adhesive/spacer medium m0 and the workpieces W is thenvibrated with the vibrator V so as to vibrate the adhesive/spacer mediumm0 and the workpieces W and make the adhesive/spacer medium m0 collidewith the workpieces W. As a result of the collision, the adhesivematerial m2 and the spacer particles m3 sticking to the adhesive layerformation medium m1 are transferred to the workpieces W. In other words,the workpieces W scrape the adhesive material m2 and the spacerparticles m3 from the adhesive layer formation medium m1, and theadhesive material m2 and the spacer particles m3 thus scraped form anadhesive layer. Subsequently, the adhesive layer formation medium m1 isseparated from the workpieces W. Such a process is repeated to form anadhesive layer consisting of the adhesive material m2 and the spacerparticles m3 and having a predetermined thickness.

In the collision of the adhesive/spacer medium m0 against the workpiecesW, the presence of the granular spacer particles m3 on the adhesivelayer formation medium m1 makes the adhesive layer formation medium m1come in contact with the workpieces W at a smaller area than in the casewhere there is no spacer particle m3 present on the surface of theadhesive layer formation medium m1. This reduces the adhesion powerbetween the workpieces W and the adhesive layer formation medium m1, sothat the adhesive layer formation medium m1 is hardly trapped on thesurface of the workpieces W. The use of the spacer particles m3effectively prevents the formation of a defect in the powder coating tobe obtained. If an adhesive layer formation medium m1 is trapped on thesurface of the workpieces W, a defect would be formed in the resultantpowder coating and, accordingly, in the continuous coating film to beformed on the surface of the workpiece after the powder coating is curedwith heat. The resultant powder coating created from the adhesive layerwill contain the spacer particles m3. Therefore, the spacer particles m3can be effectively utilized as a component of the powder coating ifparticles of the powder constituting the powder coating are used as thespacer particles m3.

When an adhesive layer formation medium m1 with the spacer particles m3adhered to it collides with the adhesive layer formed on the workpiecesW and rolls over the surface of the workpieces W, it creates a recessand scratches in the adhesive layer. The depth of the recess orscratches thus created is smaller than that observed in the case wherethere is no spacer particle m3 adhered to the adhesive layer formationmedium m1. Thus, the smoothness of the surface of the adhesive layerformed on the workpiece W is enhanced.

A powder-coating method in which a powder coating is formed by applyingpowder to the surface of the workpieces W coated with an adhesive layeris roughly described. The device shown in FIG. 1, i.e. the vibrator Vwith the container C attached to it, is used hereby as thepowder-coating device.

In this method, workpieces W with an adhesive layer, fine particles ofpowder for forming a powder coating, a powder-coating medium similar tothe adhesive layer formation medium, and other materials are put intothe container C. Then, the vibrator V is energized to vibrate thecontainer C, thereby forming a powder coating on the surface of theworkpieces W. Such a powder-coating device is disclosed in theaforementioned Japanese Patent Publication Nos. H05-302176, H07-112160and H07-136577, all of which are the patent applications of the presentapplicant.

In the above-described powder-coating method, the powder is directly, orvia the powder-coating medium, applied to the workpiece having anadhesive layer formed on its surface, and then the powder is pressedonto or into the adhesive layer by the beating action of thepowder-coating medium. Along with this process, the adhesive materialforming the adhesive layer, which is now covered with the powder, isextruded up to the surface of the powder by the beating action of thepowder-coating medium. The adhesive material thus extruded alsoundergoes the beating action of the powder-coating medium, whereby thepowder is transferred from the powder-coating medium to the workpiece.Thus, the powder continuously applied to the workpiece. Such a powderapplying process, or a powder coating process, is finished when theadhesive material constituting the adhesive layer can no longer beextruded up to the surface of the powder by the beating action of thepowder-coating medium onto the workpiece.

The powder-coating medium strikes the powder applied to the adhesivelayer on the surface of the workpiece, thereby pressing the powder ontoor into the adhesive layer to firmly fix the powder to the adhesivelayer. Also, by striking the powder attached to the adhesive layer, thepowder-coating medium extrudes the adhesive material from the adhesivelayer below the powder up to the surface of the powder and applies morepowder to the adhesive material constituting the extruded adhesivelayer, thereby creating a high-density multi-layer structure of thepowder on the surface of the workpiece. Furthermore, by colliding withthe workpiece, the powder-coating medium performs a kind of transferringaction in which the powder present on the powder-coating medium istransferred to the workpiece, thereby accelerating the deposition of thepowder on the workpiece.

In many applications of the present invention, a heat treatment isperformed after the powder coating is formed on the workpiece. Heatingthe powder coating created on the surface of the workpiece melts somecomponents of the powder coating whose melting point is lower than theheating temperature, thereby smoothing the surface of the coating film.The molten components fill the spaces between other components of thepowder whose melting points are higher than the heating temperature,thus forming a fine coating film. In this process, the curing agentcures the liquid resin, which is contained in the adhesive layer formedon the workpiece before the formation of the powder coating, and the lowmelting point components of the powder coating, which has been melted bythe heat. Thus, the heating process turns the powder coating formed onthe workpiece into a smooth, strong coating film. The curing agent usedhereby is added to both the adhesive material for forming the adhesivelayer and the powder for forming the powder layer, or only to thepowder.

A more specific example is described below.

An epoxy resin was used as the liquid resin. To reduce the viscosity ofthe epoxy resin, a reactive epoxy diluent was added to the epoxy resinby a ratio of 30:100. Dicyandiamide was used as the curing agent.Spherical particles made of acrylic resin and having a diameter of 5 μmwere used as the spacer particles. Zirconia balls having a diameter of 1mm were used as the adhesive layer formation medium. Ten kilograms ofadhesive layer formation medium, 4 g of spacer particles, 20 g of epoxyresin with reactive diluent added to it, and 2 g of curing agent wereput in the container C (capacity: 31) mounted on the vibrator V, and thecontainer C was vibrated for ten minutes to form an adhesive layer madeof the epoxy resin with the reactive diluent on the adhesive layerformation medium and adhere the spacer particles to the same medium.Then, the adhesive layer formation medium with the adhesive layer andthe spacer particles adhered to it was again put in the container Cmounted on the vibrator V, and twenty pieces of MQ bonded magnets havingan outer diameter of 20 mm, an inner diameter of 18 mm and a height of 7mm were also put in the container C, which was then vibrated for oneminute. As a result, a uniform adhesive layer having a thickness of 2 to3 μm was formed. Subsequently, the MQ bonded magnets with the adhesivelayer formed on it were put into a container for forming the powdercoating and thereby vibrated. The type and size of the vibrator and thecontainer hereby used are the same as used previously for forming theadhesive layer. Three kilograms of rubber-lined spherical aluminaparticles having a diameter of 0.5 mm as the powder-coating medium, and30 g of a powder mixture composed of epoxy powder having an averagediameter of 5 μm and mica powder having an average diameter of 5 μm by aratio of 100:20, were put into the container, which was then vibratedfor 5 minutes. Subsequently, twenty pieces of the MQ bonded magnets withthe adhesive layer formed as described above were thrown into thecontainer, which was then vibrated for 2 minutes. Thus a powder layerwas formed on each of the MQ bonded magnets, which were then taken outfrom the container and put into a furnace to be heated for 20 minutes at180 degrees Celsius. The thickness of coating layer formed on the MQbonded magnets were within the range from 15 to 25 μm.

In the above-described example of forming an adhesive layer and a powderlayer, it was necessary to maintain the amounts of the adhesivematerial, the curing agent and the spacer particles to be added to theadhesive layer formation medium within a specific range so that acoating film having a thickness of 15 to 25 μm can be formed on thesurface of the workpiece in a stable manner. In the above-describedexample, the initial amounts of these components were as follows: 20 gof epoxy resin with reactive diluent, 2 g of curing agent and 4 g ofspacer particles. These components are consumed with the progress of theformation of the adhesive layer. Therefore, if the consumption of anycomponent has exceeded a predetermined amount, it is necessary toadditionally supply that component. Our experiment showed that the totalamount of the components added to the adhesive layer formation mediumshould be controlled to be within the range of 26±5 g with theirpercentages maintained at the specified values to obtain a coating filmhaving a thickness of 15 to 25 μm in a stable manner.

The method for forming an adhesive layer according to the presentinvention is characterized in that the liquid resin (i.e. liquidthermosetting resin) mixed with the curing agent contains no solvent.This eliminates the necessity of performing a heat treatment on theworkpiece coated with the liquid thermosetting resin to remove thesolvent and other components as in the conventional methods for formingan adhesive layer. Thus, the present invention not only shortens thetime required for the formation of the adhesive layer but alsocontributes to the conservation of energy.

The elimination of the heat treatment for removing the solvent and othercomponents allows the use of a liquid thermosetting resin that cures atroom temperature. This increases the degree of freedom of the curingagent and the base resin available, thereby widening the scope of choicefor the workpiece.

Furthermore, the present invention eliminates the unevenness in thethickness of the adhesive layer due to the evaporation of componentssuch as the solvent used as the diluent for a resin used as the adhesivematerial. Therefore, it is possible to constantly form an adhesive layerhaving a specified thickness on the surface of the workpiece, therebyimproving the evenness in the thickness of the adhesive layer amongplural workpieces and facilitating the regulation of the thickness ofthe adhesive layer.

The presence of the spacer particles on the adhesive layer formationmedium prevents the medium from being trapped onto the workpiece.

This method prevents the formation of a pool that is observed if theworkpiece is dipped in a reservoir containing a liquid resin used as theadhesive material or the liquid resin is sprayed onto the workpiece.Thus, an adhesive layer having a uniform thickness is formed on theworkpiece.

In the method described thus far, an adhesive layer having apredetermined thickness is formed on a workpiece by repetitive processesof making an adhesive layer formation medium collide with the workpieceto transfer an adhesive material and spacer particles from the adhesivelayer formation medium to the workpiece and then separating the adhesivelayer formation medium from the workpiece. The amounts of the adhesivematerial and the spacer particles that have been transferred from theadhesive layer formation medium to the workpiece can be calculatedbeforehand from the area of the target section of the workpiece on whichthe adhesive layer is to be formed and the average thickness of theadhesive layer to be formed on that section. Accordingly, after theworkpieces W that have been coated with the adhesive layer by theadhesive layer formation device shown in FIG. 3 is taken out from thecontainer C, the amounts of the adhesive material and the spacerparticles consumed by the workpiece during the process are calculated,and the material and the particles are added to the container C by theamounts calculated, using a dispenser or similar apparatus, tosupplement the adhesive layer formation medium with the adhesivematerial and the spacer particles by as much amounts as transferred tothe workpiece. Now, with the adhesive layer formation medium having thesame amounts of the adhesive material and the spacer particles as in theinitial condition, it is possible to put a new workpiece into thecontainer C and repeat the process of forming the adhesive layer havinga predetermined thickness on the surface of the workpiece.

Another example of the device for forming an adhesive layer is describedwith reference to FIG. 4.

A workpiece W held by a suction pad 1 is set in the container C holdingan adhesive layer formation medium coated with an adhesive material sothat the workpiece W comes in contact with the adhesive layer formationmedium coated with the adhesive material. A pipe 2 leading to thesuction pad 1 is fixed to a support member 3, and a flexible pipe 4 isconnected to the pipe 2. The flexible pipe 4 is connected to an air pumpsystem 6 via a valve 5. When the valve 5 is opened, the workpiece W issecurely pulled by the suction pad 1. Then, as described above, themotor v4 is energized to vibrate the container C mounted on thevibrating plate v3 so as to form an adhesive layer on the workpiece W asin the case of FIG. 3. It is also possible to horizontally vibrate oroscillate the support member 3 to accelerate the formation of theadhesive layer on the workpiece W or improve the uniformity in thethickness of the adhesive layer. The present method is applicable to thepainting of products having a relatively large area, such as the body ofa cellular phone or a notebook computer.

1. A method for forming an adhesive layer comprising: putting adhesive layer formation media coated with adhesive materials and at least one workpiece into a container; vibrating or stirring in the container the adhesive layer formation media and the at least one workpiece so that the adhesive layer formation media and the at least one workpiece collide with each other, thereby forming an adhesive layer on the surface of the workpiece.
 2. The method for forming an adhesive layer according to claim 1, further comprising forming the adhesive layer on a surface of the at least one workpiece having little or no adhesive material applied to it.
 3. The method for forming an adhesive layer according to claim 1, further comprising forming an adhesive layer on the adhesive layer formation media, the thickness of the adhesive layer being maintained within a specific range so that the adhesive layer to be formed on the at least one workpiece has a uniform thickness.
 4. The method for forming an adhesive layer according to claim 1, wherein the adhesive material contains a liquid material.
 5. The method for forming an adhesive layer according to claim 4, wherein the adhesive material contains a liquid resin.
 6. The method for forming an adhesive layer according to claim 5, wherein the liquid resin contains a curing agent.
 7. The method for forming an adhesive layer according to claim 1, wherein the adhesive material contains spacer particles.
 8. The method for forming an adhesive layer according to claim 1, wherein the adhesive material consists of a substantially non-volatile material.
 9. The method of claim 1 further comprising: putting the at least one workpiece with the adhesive layer, particles of powder, and powder-coating media into a container; and vibrating the at least one workpiece with the adhesive layer, particles of powder, and powder-coating media in the container.
 10. The powder-coating method according to claim 9, wherein the adhesive material contains spacer particles, which consist of particles of the powder. 